So this is totally not a robot in the traditional sense, but it was a fun project to do. Two Light Sensors (in proximity mode) take a reading every time a ball rolls in front. By keep track of if the left hand side or right hand side delivers the ball, it can keep statistics on how ‘fair’ the kids toy is.
Full blog post write up, including RobotC source code can be found here - http://www.damienkee.com/home/2015/12/22/testing-the-tumblebug-ev3-and-vex-iq.html
cheers
damo